1. Field of the Invention
The present invention relates to an optical displacement sensor, and an external force detecting device, and more particularly to an optical displacement sensor to detect positional displacement of a measurement object in relation to a reference object by sensing displacement of a light receiving position, and to an external force detecting device to detect an external force applied to the measurement object according to an output signal from the optical displacement sensor.
2. Description of the Related Art
An external force detecting device, such as a six-axis optical force sensor, is conventionally known, in which an amount of displacement of an action section for receiving an external force, namely a measurement object, relative to a support section for supporting the action section, namely a reference object is detected by an optical displacement sensor, and an external force applied to the action section is calculated according to an output signal from the optical displacement sensor.
For example, a six-axis optical force sensor comprises optical displacement sensors to measure displacements, based on which forces are calculated with respect to six-axis directions. Such a six-axis optical force sensor comprises three optical displacement sensors, each of which includes an optical sensor unit and is capable of measuring displacements with respect to two-axis (X and Y) directions. The optical sensor unit comprises a light emitting diode (LED) as a light source and a photodiode (PD) assembly as a light receiving element such that the LED opposes the PD assembly with their respective optical central axes aligned to each other. The PD assembly is composed of four PD's and receives light emitted from the LED at its center area equally shared by the four PD's, whereby displacement of light receiving position at the PD assembly, that is to say relative positional displacement between a component attached to the LED and a component attached to the PD assembly can be detected in the optical displacement sensor. In such a six-axis optical force sensor, six-axis force applied between the component attached to the LED and the component attached to the PD assembly is calculated according to an output signal from each of the optical displacement sensors.
FIG. 1 is a plan view of a conventional six-axis force sensor disclosed in Japanese Patent Application Laid-Open No. H03-245028. A six-axis force sensor 1 shown in FIG. 1 is structurally composed of a cylindrical main body, and top and bottom lids (not seen). The main body is constituted basically by a frame 5, which integrally includes: a cylindrical support section 2; an action section 3 located centrally inside the support section 2 and adapted to receive an external force; and three elastic spoke sections 4 crookedly structured so as to be duly deformed elastically in all directions and supportably connecting the action section 3 to the support section 2. The frame 5 is made of a single piece of an aluminum alloy material and shaped by cutting and electric discharge machining. The support section 2 and the action section 3 are fixedly connected respectively to two components to which a measurement force is applied, and when the applied force acts on the six-axis force sensor 1 structured as described above, micro-displacements with respect to three-axis directions and micro-rotations with respect to rotational directions thereabout are generated between the support section 2 and the action section 3.
The six-axis force sensor 1 further includes three light sources 6 disposed at the inner circumference of the support section 2 at 120 degree intervals (i.e. at an equi-angular distance), and three optical sensors (light receiving elements) 8 disposed at the action section 3 at 120 degree intervals (i.e. at an equi-angular distance) so as to oppose respective three light sources 6 with mutual optical axes aligned to each other. Each optical sensor 8 and each light source 6 disposed opposite to the optical sensor 8 make up an optical sensor unit (optical displacement sensor) 9.
FIG. 2 is an explanatory perspective view of the optical sensor unit (optical displacement sensor) 9 of FIG. 1. As shown in FIG. 2, each of the optical sensors 8 is constituted by a PD assembly composed of four PD's 8a. The light sources 6 disposed opposite to respective optical sensors 8 are each constituted by an infrared high-intensity LED with a pinhole aperture provided at its front face, and light emitted from the LED and passing through the pinhole aperture propagates diffusedly and impinges on the center portion of the optical sensor 8 so as to be substantially equally irradiated on all the four PD's 8a. If the support section 2 and the action section 3 are displaced relative to each other by an external force, then the light emitted from the LED is irradiated unequally on the four PD's 8a, and light amounts received at respective four PD's 8a are measured for calculation of relative displacements with respect to X and Y axis directions. And, the six-axis force sensor 1 calculates forces with respect to six-axis directions according to the above-calculated relative displacements, and a signal is outputted therefrom.
The aforementioned conventional six-axis force sensor, i.e., external force detecting device has the following problems. Since LED'S, and PD assemblies to receive light emitted from the LED's are fixed respectively to different sections (specifically in FIG. 1, the light sources 6 (=LED's) are fixed to the support section 2 while the optical sensors 8 (=PD assemblies) are fixed to the action section 3), wires connected to the LED's and the PD assemblies are installed apart from each other thus making the wiring work troublesome, and also alignment work of optical axes between the LED and the PD assembly is also very troublesome.